Intestinal Parasites

Intestinal parasites are very common in both dogs and cats, and especially puppies and kittens, since egg transmission can occur transplacentally, transmammarily, through grooming, or regurgitated meals. In adult dogs and cats egg transmission can occur through direct ingestion of the eggs from the environment, through ingestion of a definitive (an animal harbouring a sexually mature parasite), paratenic (an animal serving as a transport for an immature parasite with no development taking place) or an intermediate host (an animal used during the immature stages of the parasite’s life cycle to continue their development), like a flea, mouse, bird, snail, etc., percutaneously (internal access obtained through the skin), from grooming other infected animals, and through grooming themselves (licking paws that have stepped in infected feces or soil). For the reasons above fecal analysis is the number one most common laboratory test run in a small animal clinic. At the Victoria Road Animal Hospital we recommend a fecal analysis for any new pet or puppy or kitten, and then yearly for adult pets. If your pet has tested positive for an intestinal parasite then we will contact you and prepare the appropriate medication that targets that parasite. We will also ask that you bring in another fecal sample 3-4 weeks after treatment has been finished to ensure that the medication has cleared up all parasite eggs.

LISTED BELOW ARE THE MOST COMMON INTESTINAL PARASITES FOUND AT THE VICTORIA ROAD ANIMAL HOSPITAL.

Roundworms (ZOONOTIC)

There are 3 different species of roundworm or ascarids that readily affect dogs and cats – Toxocara canis (affects dogs only), Toxacaris leonina (affects both dogs and cats), and Toxocara cati (affects cats only). The eggs of all three species can remain infective in the soil for months to years even through the winter, and can be transmitted to humans. Both Toxocara canis and Toxocara cati eggs can be transmitted through direct ingestion or ingestion of a paratenic host.

Toxocara cati life cycle

Toxocara cati life cycle

Step One:Toxocara eggs are passed in the host’s feces. If a fecal sample is tested, the eggs can be detected. The embryonic worm develops in the outdoor environment inside its microscopic egg for one month before it becomes able to infect a new host. If environmental conditions are favorable, it takes about a month for the egg to become infective but Toxocara eggs are famous for weathering harsh environmental conditions. Eggs can remain infective for months to years.

Note: Fresh feces are not infectious.

Step Two: The egg containing what is called a second stage larva is picked up orally by a cat or by some other animal. The egg hatches in the new host’s intestinal tract and the young worm burrows its way out of the intestinal tract to encyst in the host’s other body tissues. If the new host is a cat, the life cycle proceeds. If the new host is a member of another species, such as a rodent, the larvae wait encysted until the new host is eaten by a cat.

Step Three: These second stage larvae can remain encysted happily for years. If the host is a cat, though, most larvae waste no time encysting and continue their migration straight to the lungs. The majority of the incoming larvae have reached the cat’s lungs by the third day after infection. Those larvae that stay behind encysted do so in the cat’s liver. Once they get to the lung, they develop into third stage larvae and burrow into the small airways, ultimately traveling upward towards the host?s throat. A heavy infection can produce a serious pneumonia. When they get to the upper airways, they cause coughing. The worms are coughed up into the host’s throat where they are swallowed, thus entering the intestinal tract for the second time in their development.

If the host is a nursing mother, second stage larvae can migrate to the mammary gland instead of the lung. Kittens can thus be infected by drinking their mother’s milk. Larvae that had encyst in the liver and gone dormant will re-awaken during the host’s pregnancy, continuing their migration just in time to infect the nursing kittens. In this way, a well-dewormed mother cat can still infect her kittens.

Note: When cats are dewormed, this affects only worms in the intestinal tract. It does not affect encysted larvae. It is very difficult to prevent mother-to-kitten transmission and routine deworming is not adequate.

Step Four: Once back in the intestine, the larvae complete their maturation and begin to mate. The first eggs are laid about one week after the fourth stage larvae have arrived in the intestine and about 4 to 5 weeks after infection has first occurred. From here the cycle repeats.

Toxocara canis life cycle

Toxocara canis life cycle

Step One:Toxocara eggs are passed in the host’s feces. If a fecal sample is tested, the eggs can be detected. The embryonic worm develops in the outdoor environment inside its microscopic egg for one month before it becomes able to infect a new host. If environmental conditions are favorable, it takes about a month for the egg to become infective but Toxocara eggs are famous for weathering harsh environmental conditions. Eggs can remain infective for months to years.

Note: Fresh feces are not infectious. Soil contaminated with feces is infectious.

Step Two: The egg containing what is called a second stage larva is picked up from the dirt by a dog or by some other animal, usually in the course of normal grooming. The egg hatches in the new host’s intestinal tract and the young worm burrows its way out of the intestinal tract to encyst in the host’s other body tissues. If the new host is a dog, the life cycle proceeds. If the new host is a member of another species, the larvae wait encysted until the new host is eaten by a dog.

Step Three: These second stage larvae can remain encysted happily for years. If the host is a dog, the larvae mostly encyst in the host’s liver. When the time comes to move on, the larvae excyst and migrate to the host’s lungs where they develop into third stage larvae. They burrow into the small airways and travel upward towards the host’s throat. A heavy infection can produce a serious pneumonia. When they get to the upper airways, their presence generates coughing. The worms are coughed up into the host’s throat where they are swallowed, thus entering the intestinal tract for the second time in their development.

If the host is pregnant, the larvae do not migrate to the lung after they excyst; instead they home to the uterus and infect the unborn puppies. The second stage larvae make their way to the puppies’ lungs to develop into third stage larvae.

If the host is a nursing mother, second stage larvae can migrate to the mammary gland instead of the lung after excysting. Puppies can be infected by drinking their mother’s milk, although due to the intrauterine cycle described above, the litter would probably already be infected. Note: When dogs are dewormed with traditional dewormers, this affects only worms in the intestinal tract. It does not affect encysted larvae. It is difficult to prevent mother to puppy transmission and routine deworming is not adequate. It is possible to prevent infection in unborn puppies by using a specific daily protocol of fenbendazole or with the new generation products containing moxidectin (your veterinarian can provide details).

Step Four: Once back in the intestine, the larvae complete their maturation and begin to mate. The first eggs are laid about one week after the fourth stage larvae have arrived in the intestine and about 4 to 5 weeks after infection has first occurred. From here the cycle repeats.

Hookworms (ZOONOTIC)

There are 3 different species of hookworms that readily affect dogs and cats – Ancylostoma caninum (affects dogs only), Ancylostoma tubaeforme (affects cats only), and Uncinaria stenocephala (affects both dogs and cats). The eggs of all three species can live in cool, moist soil for several weeks, and can be transmitted to humans. Eggs can be transmitted through direct ingestion, percutaniously, transplacentally and transmammarily.

Tapeworms (only Dipylidium caninum is ZOONOTIC)

There are 3 different species of tapeworms that readily affect dogs and cats – Taenia pisiformis (affects dogs only), Taenia taeniaeformis (affects cats only), and Dipylidium caninum or flea tapeworm (affects both dogs and cats). Generally, tapeworms are diagnosed by owners finding and bringing in dried out tapeworm segments called proglottids (they look like grains of rice) found in the perianal area of their pet or in the bedding of their pet.

Both Taenia spp. and Dipylidium caninum are transmitted through a definitive host (your dog or cat) ingesting an intermediate host, where the intermediate host differs for each. For Taenia pisiformis, the intermediate host is either a rabbit or ruminant, for Taenia taeniaeformis, the intermediate host is a rodent, and for Dipylidium caninum, the intermediate host are fleas or biting lice.

Giardia (ZOONOTIC)

Giardia intestinalis (aka Giardia lamblia) is a one-celled parasitic species that affects the intestines of both animals and humans. In humans Giardia is a common cause of what is commonly known as “Traveler’s Diarrhea” or “Beaver Fever”. There are two forms of this species, the fragile feeding form called a trophozoite exists in the gut of infected species and the hardy cystic form, is shed in feces and can survive for several months in the environment, particularly in water and damp environments.

Coccidia – Isospora canis/felis

Coccidia are single-celled organisms that infect the intestine. They are also not visible to the naked eye. Coccidia infection causes a watery diarrhea that is sometimes bloody; it can be a life-threatening problem, especially to a young or small pet. Oocysts (pronounced o’o-sists), like those shown above, are passed in stool. In the outside world, the oocysts begin to mature or sporulate. After they have adequately matured, they are infective to any host (dog or cat) that accidentally swallows them. To be more precise, coccidia come from fecal-contaminated ground. They are swallowed when a pet grooms/licks the dirt off. In some cases, sporulated oocysts are swallowed by mice and then the host is infected after eating the mouse. While there are species of coccidia that can infect people (like Toxoplasma and Cryptosporidium, for example), the Isospora species of dogs and cats are not infective to people.